Performance analysis of a three-phase induction machine with inclined static eccentricity

Fault diagnosis is gaining more attention for electric machines running critical loads, whose sudden breakdown can result in unpredictable revenue losses. Consequently, the motor drive systems with fault diagnostic and prediction features are of great concern and are becoming almost indispensable. Among all kinds of common faults, quite a few have relationship with unequal air gap. So far, work on detection of eccentricity-related faults in induction and synchronous machines has been well documented. However, a few are reported on faults resulting from axial nonuniform air gap. This paper investigates the performance of a three-phase induction machine with nonuniform static eccentricity (SE) along axial direction or inclined SE. A variant of modified winding function approach is applied to study this fault. The relationship between the number of rotor bars and poles, and the existence of fault-related current harmonics is discussed. It is shown that inclined eccentricity also demonstrates similar characteristics such as circumferential nonuniform air gap (SE). More importantly, it has been proved conclusively that inclined eccentricity symmetric to the midpoint of the machine shaft cannot be recognized from the current spectrum and would therefore require some other form of detection. Finite-element results to verify the inductance values used in simulation are also presented. The analysis is supplemented by the stator current spectra obtained from simulated results for different load and fault conditions. Finally, a four-pole 45-rotor-bar 2-kW induction motor is used to validate the theoretical and simulation results experimentally. Both current as well as vibration spectra are presented.